Electrical apparatus



Patented May 12, 1925.

UNITED STATES PATENT. orrlcu.

JOHND. HILLIARD. or sOHENEcTAnY, NEW roar, AssIGNOB. To GENERAL ELECTRIC COMPANY, A CORPORATION or NEW YORK.

ELECTRICAL APPARATUS.

Application led October 23, `1919. Serial No. 332,821.

To all lwiz/mn, t may concern: v

Be it known that I, JOHN-D Immun, a citizen of the United States,` residin at Schenectady, county of'Schenectady-, tate of New York, have invented certa1x1'"'new and useful Improvements in Electrical Ap` paratus, fication. I

My invention relates to electrical apparatus in which the parts thereof are surrounded by an insulating Huid, such as il, and particularly to Velectric switches havin contacts separable in an insulating fini The object of my invention is to provide a novel and im roved slivitch of' this general type in whic dangerous pressures within the vessel are eliminated, throwing of oil from the switch is prevented,-the possibility of secondary danger of impalringtheinsulating lproperties of the oil is overcome, and which consists in vgeneral of an entirely new structure whercbv the interrupting capacity of of which the following is a speciswitches of the oil-break type may be greatly increased.

Switches in which the contacts are separat-ed beneath the surface of an insulating fluid, such as oil, have been called upon to open circuits of constantly4 higher voltage systems and of not works constantly increasing in size and amount of energy to he interrupted, until in 'thel switches now in use, various limitations have been met which mustbe solved before such switches 155 may be used in the resent high energy circuits and the possib y higher energy circuits-of the future. Heretofore, the problem of interruptingcircuits by a switch ot-thc oil-break type has not received the Wcareful `study which 'the subject deserves and, as the gresult, tl'ierefore, of extensive tests, have arrived at certain fundamental principles v nich i1 is necessary to incorporate in. order that modern oil-break switches 45, will operate with a gretly increased rupturing capacity sutlcic'nto fulfill modern and future requirements.

When an are is drawn in an insulating f'uid, such as oil, in the operation of an 5U oil-break switch to interrupt. a circuit, sonic of the oil is vaporized and some dissociated by the heat of the arc and in vthe orrn of exerts luigi-l pressures upon the gas explosions is avoided,

Y perature.

cil vessel m a very short interval of tlme. It has beerufound from tests made that the `volume of gas' generated depends upon the KVA interrupted, the character of the load and the characteristics of the breaker. AThis volume of gas'formed produces two separate stresses, iirst a severe hammer blow or impulse propagated at high speed through the'oii mass acting to stress the tank, and second, slower stresses produced by the expansion of the gases and by secondary gas explosions occurring in the air chamber above the oil. These second stresses are usually manifested by blowing of oil out of the'tank and by distortion of the tank, The

interrupting capacity of an 'Oil-break switch, having an ample break distance, de-- 7U pends upon the pressure which theoil tank will stand and, okthrqthings being equal, this pressure. varies 'withthe volume of gas produced within the tank.

In Oil-break switches heretofore used, the' 75 volume of gas generated by the are, as" the switch is opened, rises to the airl chamber above the oil. It has been the customary practice in some types of switches to arrange baiiles provided with openings within'the im oil vessel in an effort to cool the gases and to prevent the oil from being blown out of the vessel by the rapidly expanding gase's.A The air chamber above the oil is'custom- 'u1-ily openedY to the air through4 suitable 85 small openings or clearance spaces izo-permit the. exit of gases but to prevent the escape of oil. In switches of this type, the volume of gas generated is large, particulai-ly on modern high potential circuits vand im the pressure cxerted'is high,'often dirupting the oil vessela'nd distorting the bathing means` Furthermore, venting the-'air chamber over vthe oil to the air, is found to permit of condensation of moisture within the chamber,'because of changes of tem- This moisture in condensing falls intothe oil and greatly impairs its insulating properties. Again the chamber above u1@ ou is Often fined with an @Xplosiv mix- 1 ture of air and gases. lThe rlsin of hot gases through the oil, due to a susequent opening of the switch, has caused serious explosions due to the ignition, by the hot gases, of the explosive sgs'ieo'lisi'fiihtnres lo existing in the air chamber. These explopurpose, I provide the switch with expansive gaseous mixtures have also been ignited by static sparks.

In the switch .of in invention these undesirable and limiting eatures have been over- `come. This switch'is provided with means whereby the gases evolved as the switch opens, may expand without greatly increasing the pressure within the vessel and Without greatly accelerating the oilmass to produce sudden or impulse stresses. For this sion chambers containing a compressible fluid such as air or in'ert gas. The oil is forced into the expansion chambers by the pressure of the gas formed bythe arc when the contacts separate, thus producing a elishioning effect to' relieve the pressures otherwise exerted upon the oil vessel. The oil vessel in wliichthe contacts separate is also completely filled with oil, thus eliminating the air chamber in which moisture might be Acondensed and in which secondary exploV sions may occur. I also provide means for cooling the gases as they rise to the top of lthe oil vessel and for permitting their A exit from the switch through an opening con-- trolled by a normally closed valve. The switch enibodyingimy invention is also provided with means to maintain the main oil vessel completely filled with oil, thus preventing gases from becoming entrappedI The. normal pressure' within 'the'y therein.' tank may be kept constant and at any pres-` sure desired. I thus provide a switch iii which the disadvantages of existing switches are overcome, and by preventing stresses within thc tank dueto gas formation and deceleration of the oil -mass,` I provide a switch with a greatly increased interrupting capacity. The principles of my invention are also applicable to transformers in which' the windings are located within a vessel containing oil and in which gases. may be formed by static sparks. g

rlhe novel fea-tures which I believeto be characteristic of my invention will bc definitely-indicated in the claims appended hereto, while the features of construction and inode of operation will be understood by reference to the following description .taken in connection with the accompanying drawings which sho'w the preferred embodishows the -applicationj-f'my. invention to vanatliertype of oil-break switch.

In Fig. 1 my invention is shown embodied in a switch or" the oil-break type comprising an insulated tank or vessel 1 adapted to contain oil or other insulating fluid. The fixed contacts 2of the switch are carried upon suitable insulating members o r-busliings 3 supported by thecover 4 for the vessel. .Cooperating with the fixed contacts 2 are movable contacts 5 carried by -a bridging member 6. The bridging member is carried by an insulating rod 7 extending through the top or cover 4 of the oil vessel 1 and is adapted to be actuated by any suitable operating mechanism, not shown, to move contacts 2 and 5. into and out of engagement to control the circuit through the switch. In the form ofswitch shown in Fig. 1, the

, fixed contacts 2 are surrounded by explosionf or compression chambers 8 provided with insulated openings through which the contacts 5 are movable. These contacts 'are, preferably, of the rod or well known, to store up-pressure durin the .initial opening movement to direct a last of oil into the are path as the movable oontact leaves the' chamber. Supported from the bottom of the explosion chambers 8 are insulating barrier members 9 of cylindrical shape Vwhich surround the chambers and supply the necessary insulation.

lunger type. `These explosion chambers 8 unction, as is Within the tank or vessel l is provided a i casing-or barrier 1() substantially concentrically disposed and extending nearly to the bottom of the vessel but spaced away from the sides of the vessel to providean annular space or chamber 11.. The barrier 10 is properly insulated or may be formedof insulating material. The chamber 11 is hermetically closed at the top by an annular member 12. The .chamber 11 formed bybarrier l0 constitutes an 'expansion chamber or shock absorbing means for the switch, as will be described hereinafter and also serves as a. means whereby the level of the oil may be varied withinthc vessel 1 and hence the pressure within the vessel may be varied, An outlet 13 is provided communicating with the top of chamber l1 which may bev opened or closed so that. with the requisite amount ot oil or other insulating fluid WithlUJ llt)

in the tank 1, may be admitted thereto, i

moreover air or gas pressure can be `admitted through the outlet 13 to force the oil down in'the annular chamber 11 to some- .le`vel such as indicated at a or until the level of the oil within the een* 'l or main portion of the tank is at any lie-igv desired. In the preferred embodiment of my invention, the pressure within the chamber 11 is suicient to maintain the oil level at the-top otl the vessel and against cover 4 so that the tank 1 is completely filled with oil .with no air chamber above thej oil level. elimination of the ordinary air chamber,

With ,the

there is no opportunity for condensation of moisture to impair the insulating properties ofthe oil as there is no air in the tank above the oil, level. 'Iliere is also no opportunity for` secondary explosions to occur due to the ignition of explosive gaseous mixtures above tliefoil by subsequently rising. hot gases or bystatic sparks.' Y

By exerting further pressure through out- -10 let13, any pressure desired may be exerted uponthe oil within' the tank 1, the level of 'the oil'rin chamber 11' giving 'an indication ofvftheA volume of gasfwitliin the expansion chambers. For indicating the level o the 15, oil= within the chamber A11 and hence the jvolume'ofvcompression space, I provide a laight 'gauge or level indicator 14 comprising Afa. ollon7 .upright tube 15 of transparent material, in` communication with the top of "chamber/11 andthe lower end of the tank 1. Y Itis apparent 'that by suitable calibration, the;V level o-fthe oil in the tube 15 and hence inV cliamberfll may be controlled to maintainltli'e tank l completelyiilled with oil at anydesired/pressure. If desired, inert an 'hydrous gas may beused Within chamberll.

Byga 'spite epressure regulating means connectediftoioutlet 13, the normal pressure withn-thetank may be maintained constan at any desired value.

` .'Ilheoperation oit an oil-break switch of "L'tlie, rior art with an oil vessel completely filledivith oilwould cause the destruction .ofthe switch due to the stresses developed -by -t he,volume of gas evolved, but I. have pi'oiidedmeans to meet this exigency in the 4-""'switc`li .structure embodying my invention. In this'switch I have provided shock absorbing'means for greatly. reducing the stresses 10 produced as Athe switch: operates and thus greatly increasing .the .energy which the fs'witchrcan interrupt; This shock absorbing means: comprises chambers 'substantially filled with acompressible Fluid such as air or .inert gas 'held sealed iii the chambers' or entrapped in position by .the oil. These `cliaiiibers may have a variety of forms and are distributed within the oil tank so as to be iimmediately available and of a capacity to take -cai'e of the maximum volume of gas which' maybe evolved.l

5" In Fig. 1, I have shown combined in one switch, vseveral formsofiexpansion chambers. One form in which my shock absorb-v ing means is used.'consists of chambers 16 mounted substantiall concentric With the 'tanlrl and supporte byiupriglits or studsl 17 secured to the casing or -barrier 1:0. These chambers 16, in the form shown, con-V 60 sist-Zot inverted 1l-shapedA annular rings spa'fed apart and mounted ,one/above the-- --"--otliei. 'These annular chambers at .frequent intervals are held rigidly in osition and spaced relation, by insulating locks 18 ofl i5 a similar configuration, to which the studs 17 are secured, asis -bestshown Fig'. 5. f A sectional View of the supporting'structui'e f' for the chambers 16 is shown in Fig. 1. TheA chambersl .extend around tlie'ta'nk 1 with# in. the central enclosure formed by barrier 10 andpreferably extend from the bottom to the top of the barrier 10 at certain spaced intervals. Each chamber is shaped to form a pocket which is substantially filled with air or inert gas held sealed or entrapped by 'the oil with which the vessel is filled.. 'lhe air in "these chambers isada lted to be .com-A pressed by the oilto provi ea cushion action, and to provide a means whereb f the oil may move'by the pressure exerte .by the evolved gases, the air thus providing anexpansion means limits the stresses within the vessell. In a similar waythechamber 1l produced by barrier 10 alsojacts as Van ex pansion chamber, pressure of, the oil 'compressingthe air or gas withinthe chamber and permitting of movement of oil within the tank with a consequent marked, i'eduction in stress.

To still further provide room for expan sion of .the oil, I provide a receptacle or expansion chamber -19 ofa dome coniguration open at the bottom and movably' supported upon pins 20. This chamber is preterably centrall dis osed near the bottom of the oil vesse ladgacent the lower end of barrier' 10. The pins 2O are secured to the bottom of the vessel and extend up through suitable channels 2l in the chamber 19. The

chamber 19 is freely movable, along pins 2O but is limited in its upward movement by stops or nuts 22 threaded on the '1 ends of' pins 20 andl adjustable thereon.. Normally." due to' the air or inert gas filling chamber 19, the chamber floats in the position, shown in Fig. 1, against stops 22. Upon opening of the switch, the oil mass in moving forces the chamber` 19 doi'vri and the oil up int-o the chamber thereby compressing the air within the chamber 19 and providing a space for the oil to be displaced by the gas from the arc. i

It is thus apparent that iii the switch shown in Fig. 1 three types of expansion chambers are shown, the annular chambers 16, the chamber 11, and chamber 19. These chambers are all below the oil surface and contain air. or inert gas which is sealed or enti'apped 1n the chamber by the', insulating liquid. jTliis air or gas is easily compressible. and when the switch opens and the gases are formed by the arc, the oil is forced into-the expansion chambers to compresslio gas in` the chambers.

The volume of oil entering the chambers is substantially equal to .the volume of gas generated.` The movementpf the oil into the chambers thus pro; i

A within the tank 1 and normally closing an closes to prevent anv 'oil from being blown outlet from the tank'. As 'the gases rise to the top of the tank 1, the level of the oil is forced down and ctnsequentlyI the float 24 falls andl opens the outlet permitting; the'valve 23 to furnish an exit forall the gases. lVhen all the gas has been expelled and the level. of the oil rises to normal position, the ioat 24 automatically from the switch. There is also carried near -the top of the tank 1 above 'the'annular chambers 16 a cooling means for the gases which consists of screens or perforated members 25 be- .tween which is a layer of porous material 26 such as gravel or like material. This screen vor battle'ser-ves to break upA the gas Vmass evolved, into small streams, and' acts to cool the same before its exit from the switch. In my copending application S. N. y 3,440 filedFeb.' 8,' 1921, I claim broadl v an oil switch having: a gravel bathe;4 At the same' time the so-called chimney effeet is eliminated in which the gas evolved f rises in a large highly heated volume. `I n order to facilitate theremoval of oil, an outlet 27' is provided at thebottom of the tank 1.

Instead-of using al1 the formsofexpanf sion chambers shown in Fig. 1, I may uset anyone 0r more forms as desired, depending on the energy of the circuit to be 'in terrupted. In Fig. 2 for instance, the barrier 10 is used alone to provide the `expansion chamber 11" with its attendant functions and in this type of switchthe explosion chambers 8 are'omitted. In Fig.

3 the same type of switch is shown utiliz-I ing the expansion chamber 19 alone, while 1in Fig. 4 an explosion chamber type of switch is shown with the expansion chamber 1.1 in combination with the annular chambers 16.

The ri'nciples of my invention are equally app icable to explosion or4 pressure .retaining chambers installed as a part of hlgh tension switches as well as to the oil vessels themselves,- as the explosion `chamber may be consideredas a small high pressure switch within the main switch. In the explosion lchamber type of switch, the are is drawn between the fixed' and movable contacts which' are surrounded by the explosion chamber. A high pressure is developed within the chamber until the movable contact moves out of the chamber whereupon the pressure is then utilized to blast a'current of oil out of the opening to interrupt the circuit. unless the blast of oil 1s delivered with great rapidity, due to great pressurefits interrupting effect is impaired. According therefore, to the principles of m. invention, l may provide expansion cham ers within tl vexplosion -chamber into whichthe oil wit 1in the ,explosion chamber may How due to the excessive pressure developed; providing these expansion chambers, permit of a greater gas generation within the pres- In these explosion chambers,

sui-e retaining chamber without injury to the chamber-and hence a greatly. increased interrupting capacity of the switch. In Fig. 6,' I have shown a pressure retaining or explosion chamber 28 surrounding. the

fixed contacts for the switch, `it being understood that such a chamber could be substituted for Athe explosionochamber 8 in the switch shown invFigs. 1 or 4. .This chamber is of usual steel construction suitably insulated with an opening in the lower wall supplied by an insulating bushing 29 through which the movable contact passes.

Substantially concentrically disposed with-' in chamber 28 is an annular member 30 spaced apart from the walls of chamber -28 .forming the expansion chamber 31 for the oil.within the chamber 28.- This member 30 may be of insulating material or may consist of insulated metal. The expansion chamber 31, as has been before described, contains air or inert gas which ma be compressed topermit of expansion o the oil in the manner already 'set forth. This expansion chamber 31 may be of the form shown or may consist of one or more annular rings of .the type shown by chambers 16 of Figs. 1 and 4. In order Ato permit all the gases evolved to escape from the explosion chambel' 28, I provide a small opening or bleed' hole, 32'at the top of the chamber which permits the oil to easily fill the chamber 28 and e'o'a'pel any gases therein.4

In the. switches so far described, the `contacts have been separated' with a. downward break. My invention is" equally a plicable to upward break switches, as is sh wn Vin 7, where the oil vessel carries the' fixed contacts 2 at' the bottom of the vessel and the movable or. rod contact 5 moves upwardly through the openings provided in a-member 33. The member 33 1s suitably supported.

in position and insulated. This member.

forms below. a pressure retaining or compression t pe o i hamber in which the are 1s first rawn as the contacts separate. W'ithin this closed lchamber is substantially concentrically 'an expansion chamber 34 of the annular typej This chamber is of the inverted type similar' to -chambers 16 of Fig. l and is suitably insulated or made of insulating material itself. This chamber contains an inert gas or air 'and functions as has been described. The

pressure developed within this compression chamber is utilized in compressing the gas 1n the expansion chamber 34 solthat as the contact rod 5 moves ont `of the opening in the baille 33, a. tremendous blast of oil is i delivered into the are path to interrupt the circuit. With this construction, the oil'vessel is relieved from excessive stresses and the blast of oil is ejected intov t-he arc path during the zero part ofthe current Wave when its action is most efficient. It is understood that an oil gauge 14, screen 25 and outlet 13 may be used in connection with this type of switch, if desired, similar to that shown in 'F ig. l and anytype of expansion chamber may be substituted for the form shown. i

I desire it to be understood that the novel expansion chamber feature of myswitch, in which pressures Within the oil vessel are greatly reduced, is not limited to switches havin@r vessels completely filled with oil,

but this feature is equally applicable t'o switches embodying an air chamber above the oil surface and improves the operation of the same.

What I claim as new4 and desire to secure by Letters Patent of the United States, is

l. An oil. switch provided with a bafe composed of an aggregation of individual bodies located beneath' the normal surface of the oil andA arranged in the path of the material ejected upon the opening of the switch.

2. An oil switch comprising a vessel` adapted to contain oil, said vessel being provided with an outlet for gases formed upon an opening of the switch and a porous mass of insulatingl material located beneath the normal surface of the oil Within said vessel and forming a plurality of extended narrow passages for the escape of said gases,

3. In an electric switch, the combination of a vessel adapted to contain insulating fluid, relatively movable cooperating contarts' separable in said fluid and means located at different levels within said vessel and operative in response to .the generation of gases formed as said contacts separate to permit"displacement of said fluid'by the gases formed.

4. In an electric switch, the combination of avessel adapted to contain insulating fluid, relatively. movable cooperating contacts separable in said fluid and means surrounding said contacts `and located at different levels ivithin said vessel and operative in response to the generation of' gases formed as said contacts separate to permit displacement of said fluidby the gases formed. f,

5. In an .electrical apparatus, thel combination with a vessel adapted to contain an insulating fluid, of means Within said vessel forming a chamber, the walls of which are independent ofthe walls of said vessel, containing a gas compressible to permit ithe flow of said fluid into said chamber.

G. In an electric switch, the combination with a vessel adapted to contain an insulating fluid, relatively movable cooperating contacts separable in saidfluidfand'4 'means within said vessel formed with a 'passage in Vcommunication with' said fluid forfpermitting the gases formed as said contacts separate to displace said insulating fluid Without subjecting said vessel to excessive I and means Within said vesselformed with a chamber containing a gas held entrapped therein, said gas being compressed due to the movement of said fluid by the gases generated by the arc as said circuit is being interrupted.

8. In an electric switch,Il the combination with .vessel adapted to contain an insulating fluid, relatively movable cooperating contacts separable in said fluid, of a chamber beneath the level of the fluid in said vessel containing a gas, said gas being compressed by the oW of the insulating uid into-said chamber when said contacts separate.-

9. In an electric switch, the combination with a vessel adapted to contain an insulating fluid,l relatively movable cooperatinfr contacts separable in said fluidi, an inverted chamber in the fluid of' said vessel and containing a gas held in said chamber by said fluid, said gas being compressed by the flow of said fluid into said chamber due to the pressure of thel gases generated by the `arc when the contacts separate. t

l0. In an electric switch, he combination with avessel adapted tocontain an insulating fluid, .relatively movable cooperating contacts separable in said fluid, ,a pressureretaining chamber vsurroundnnq said con` chamber: 'within said pressure vretaining chamber` containing af'gas, said gasf bein compressed `to limit the stresses upon sai pressure retaining chamber.

i 13. In an electric switch, 1thecombination with a vessel adapted to be filled with insulating fluid, relatively movable cooperating contacts se arable in said fluid, expansion chambers distributed within said vessel containing gas sealed in said chambers by said fluid, said chambers affording sufficient spacejwithin which said fluid may .flow and .compress said gas to provide a space for the gases formed as the contacts separate.

` '14. In an electric switch, the combination.

with a vessel adapted to be filled withV an A'insulating fluid, relatively movable cooperating contacts separable in said fluid, a chamber within said vessel communicating with said fluid and containing a gas, and means for varying the gas pressure within said chamber and hence the pressure exerted upon the insulating fluid in said vessel.

15. In an electric switch, .the combination with a Vessel adapted to be filled with'an 'insulating fluid, relatively movable cooperating contacts separable in said lluid'Land :a valve held normally closed by the normal level of fluid in said vessel but automatically opened 'in response to the lowering of thclevel of said fluid'below a predetermined point to vent said vessel to the air.

16. In an electric switch. the combination with a vessel adapted tobe filled with an insulatingV fluid, relatively movable cooperating contacts separable in said fluid. and means operative by the level of fluid within said vessel to automatically veut said vessel to the air to permit the escape of gases generated within said vessel, said means operating to close said vessel to preventthe escape of oil when said gases have been expelled.

17. In an electric switch, the combination with a vessel adapted to be filled with insulating fluid, relatively movable cooperating contacts separable in said fluid, means whereby the level of fluid within said vessel may be maintained constant, means for automatically opening an outlet in response to the 'generation of gases within said vessel to permit their escape and closing said outlet when said gases are expelled, and means for providing4 a space'for the flow of the insulating fluid" by the pressure exerted by said gases whereby the stresses exerted upon said-vessel by said gases and'insulating fluid` are harmless.

18. In an electric switch, the combination with'a vessel adapted to contain an insulating fluid, relatively movable cooperating contacts separable in said fluid, and mea-ns for cooling and breaking up the gases generatedby t-liearc as said contacts separate.

com rising a gravel baille arranged below the evel of said'fluid.

' 19. In an electrical apparatus, thecom- 'bination with avessel adapted to contain an vessel, said outlet being automatically closed after said gases are expelled, and means in the path of exit of said gases for cooling the gases in their passage from said vessel.

21. In an electric switch, the combination with a vessel adapted to be filled with an insulating fluid, relatively movable cooperating contacts separable in said fluid, a chamber in said fluid containing a gas held entrapped by said fluid, and means whereby the normal volume of gas within said.chamber may be controlled to adjust tbc level of the insulating fluid in said vessel.

22. In an electric switch` the combination with a vessel adapted to be filled with an insulating fluid, relatively movable cooperating contacts separable in said fluid, a chamber containing a gas. and means whereby 'gas'inay be admitted 'to said chamber to increase the gn'cssure of fluid in said vessel.

Q3. In an electric switch, the combination with a vessel adapted to be filled with an insul-ating fluid, relatively movable cooperating contacts separai'ile in said fluid, a ineluber disposed within said vessel and spaced apartlroin the walls thereof to forni a chamber. andiueans for admitting gas to said chamber to raise the, level of fluid witbin said vessel.

2.4. In an electric switch, the combination of a vessel adapted to contain insulatingl fluid, a casing within said vessel forming therewith al gas chamber, relatively movable cooperating contacts separable in said fluid, and an automatically operated valve in said vessel constructed to open upon the accumulation of gas in the upper portion of the casing-and to close when vthe gas has been displaced. i

25. In an electric switch, the combination with al .vessel adaptedto be filled with au insulating iiuid, relatively movable cooperating contacts separable in said fluid, and

inverted substantially lU-shaped annular members within said vessel containing gas,

, said gas being compressed to provide a space forl the flow vf said fluid therein by pres# sures developed within said vessel.

26. In an electric switch, the combination with a vessel ada ted to be'illed with an insulating fluid, re atively movable cooperating contacts separable in said fluid, a chamber containing a gas, and annular members spaced apart and mounted substantially in alignment within said vessel,fsaid members' forming chambers containing gas, said gas being compressed to provide a space for the ow-of said uid therein by pressures developed within said vessel.

SI2?. In an electrical apparatus,V the combi'- nation with a vessel adapted to contain an insulating uid, co-operating switch contacts separable in said fluid, and compression chambers arranged in said vessel .to permit u Ward and downward movement of said luild by the pressure produced upon and forming a j insulating the interruption of the circuit at said contact's.

containing oil and having an outlet for the gases formed .upon the opening of thel 25., 28.` An'oil switch comprising a vessel for l porous mass supported by -said container v plurality of tortuous passages for the `escape of said gases.

29. In an electric switch, the combination of a vessel for containing oil, relatively movable cooperating contacts separable in said oil, and means for cooling and breaking u the gases generated by the arc forme as said contacts separate,Y said means comprising a receptacle having its upper and lower walls formed'of screens of material and a mass of gravel carried by said receptacle.A4

In witness whereof, I have hereunto set my handV this 21st day of October, 1919.

' JOHN D. HILLIARD. 

